1. Field of the Invention
This invention relates to an apparatus for easily drawing blood from the patient's arm or leg. The apparatus of this invention can increase the quantity of blood drawn per unit time and, therefore, is particularly suitable for joint use with blood treatment apparatus for plasma collection requiring a long period of time in blood drawing.
2. Description of Prior Art
A method generally employed for easy blood drawing from a patient's body is to use a tourniquet made of rubber tube. The tourniquet is tightly wound around the patient's arm or leg. Blood is drawn from the swollen vein in the arm between the tourniquet and the tip of arm or leg. In most cases, blood is drawn from the bent part of the elbow. In the case of extracorporeal circulation blood treatment, treated blood is returned to the patient's body through either the other arm freed from the tourniquet or a part lying upstream of the tourniquet.
Such a method as using the tourniquet is well known to those skilled in the art. However it is known that the method is inapplicable to extracorporeal blood circulation continuing for a long time by reason of the possible danger of of toxic substances remaining in the vein constricted by the tourniquet. Accordingly, when using the tourniquet, it is necessary to loosen the tourniquet periodically and then re-start extracorporeal blood circulation. However, in practice, adjustment of pressure for tightening the tourniquet during blood drawing is difficult.
On the other hand, a method of pressing the vein with a bag-like band, instead of the tourniquet, wound around the patient's arm or leg and inflated with air is now employed (Japanese Patent Laid-open No. 12195/1983 and others). According to this method, the bag-like band is connected to a tank containing pressurizing gas such as nitrogen or Freon by a tube and the pressurizing gas is fed into the bag-like band by opening an electrically driven valve connected to the tube. This method, however, is attended by the danger of toxic substances remaining in the pressed part of the vein due to constant inflation of the band, a situation similar to the application of a tourniquet. In addition, the use of pressurizing gas is dangerous to handle and causes a problem in that a sure and safe adjustment of pressure requires a large and costly apparatus.